A significant portion of ores that contain copper sulphide is chalcopyritic ore, CuFeS2, of which the most common processing method after enrichment is pyrometallurgical smelting—anode casting—electrolytic purification. Nowadays however there is also interest in the hydrometallurgical processing of copper sulphide ores, whereby the first treatment stage itself is also commonly the formation of a flotation concentrate, after which usually at least one concentrate leaching stage takes place in autoclave conditions. The other primary occurrence of copper sulphide is chalcocite, Cu2S, which is processed principally in the same way as chalcopyrite. Chalcopyrite and chalcocite generally occur in the same ore and often the amount of chalcopyrite is predominant.
The leaching of minerals containing chalcopyrite and/or chalcocite with the aid of trivalent iron in a solution containing sulphuric acid is described e.g. in WO publications 2005/042790 and 2005/005672. In both cases the oxidation of the divalent iron formed in leaching to trivalent is performed in autoclave conditions, although at least part of the concentrate leaching could be performed in atmospheric conditions. The copper sulphate solution formed in leaching is routed to conventional copper recovery.
A method for the hydrometallurgical recovery of copper from chalcopyrite and other sulphides is described in U.S. Pat. No. 4,115,221. In this method the sulphide mineral is ground to a fineness where the particle size is a maximum of one micrometer. The sulphidic solids are leached into an acidic solution, in which the amount of ferric ions is stoichiometrically sufficient to oxidise the copper contained in the copper sulphide material. Part of the iron is removed from the copper sulphate solution by precipitating the ferrous sulphate from it, after which the solution is routed to copper electrolysis. The solution exiting electrolysis, which is dilute in relation to copper, is routed to a separate stage, in which the ferrous iron still in solution is oxidised into trivalent before routing the solution back to sulphide leaching. In the method, the leaching and formation of trivalent iron used in leaching take place in different stages.
EP patent 815,270 describes a method for leaching sulphidic minerals, where the mineral also contains iron. According to the method, the mineral is ground to a fineness where the P80 is 20 microns or less. Leaching takes place by means of ferric iron and sulphuric acid in an open reactor and oxygen is fed into the reactor to oxidise the ferrous iron formed in sulphide leaching back into ferric iron. All the examples in the publication describe the treatment of flotation concentrate. The copper sulphate solution formed in leaching is routed to conventional extraction and electrowinning.
The drawback of the two last atmospheric methods described above is considered to be the fact that for leaching to succeed, the mineral has to be ground very fine, which consumes energy and thus raises grinding costs. In addition, it can be said of the latter method that with oxidation in an open reactor an excess of oxygen has to be fed in, because it cannot all be taken back into circulation.